Loan Sale and Servicing Activities and Variable Interest Entities (Cash Flows Associated with Loan Sale and Servicing Activities) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Residential Mortgage [Member]
Cash flows from sales of loans	$ 1,242	$ 1,468	$ 3,486	$ 4,385
Cash flows from repurchases of previously transferred loans	90	103	286	331
Cash flows from servicing fees	88	95	269	281
Cash flows from servicing advances recovered (funded), net	2		45	80
Cash flows on mortgage-backed securities held	574	372	1,445	1,066
Cash flows from servicing advances recovered (funded), net		(4)
Carrying value of mortgage-backed securities held	13,000	7,600	13,000	7,600	$ 8,800
Commercial Mortgages [Member]
Cash flows from sales of loans	953	1,280	2,613	3,639
Cash flows from servicing fees	34	32	100	95
Cash flows from servicing advances recovered (funded), net	19		24	25
Cash flows on mortgage-backed securities held	51	13	100	196
Cash flows from servicing advances recovered (funded), net		(1)
Carrying value of mortgage-backed securities held	$ 600	$ 700	$ 600	$ 700	$ 600